1. Field of the Invention
This invention relates to two-MCU system and a hang-up detecting method of an MCU (Micro-Computer Unit), and more particularly to a hang-up detecting method of an MCU in a two-MCU system provided with a main-MCU power-on-reset and a sub-MCU reset by the main-MCU, wherein the sub-MCU detects a hang-up state of the main-MCU, and the two-MCU system.
2. Description of the Prior Art
An example of this kind of a conventional two-MCU system is disclosed in a Japanese Patent Laying-open No.2-281367 (G 06F 15/16) laid-open on Nov. 19, 1990. The system is provided with a main-CPU and a sub-CPU, and pulses are outputted from the sub-CPU to a watchdog timer at a predetermined cycle. When the pulses are stopped, over-running of the sub-CPU is detected. Then, when detecting the over-running, a reset signal is outputted from the watchdog timer, and the sub-CPU is initialized.
A system of this prior art is applied to a DVD, a VTR, and etc, for example. In the DVD or VTR, there was a problem that the main-CPU is brought into a hang-up state because a complex control such as image or video processing is executed by the main-CPU. That is, it results in a situation of not accepting the key operation. However, according to this prior art, in the case the sub-CPU over-runs, the sub-CPU can be initialized, but when the main-CPU is hung-up, it is impossible to deal with it.
Furthermore, in the case the main-CPU is hung-up, the most that can be done is a plug is pulled out from a socket to stop a power supply and to reset. That is, it causes bother of operation.
Meanwhile, in the case the main-CPU is subjected to a hang-up, since the key operation cannot be accepted, a user determines a DVD or a VTR have a breakdown, causing a problem of sending them for repair.